Tumor-associated macrophages (TAM) are abundant in many types of cancers. Together with other stromal cell types (fibroblasts, neutrophils, mast cells, T cells, dendritic cells, endothelial cells) and matrix components (collagen, fibronectin, glycoproteins) these cells exhibit complex regulatory functions mediated through growth factors, chemokines, cytokines and angiogenesis promoting factors. There is compelling evidence that TAM respond to tumor stimuli with the release of proteolytic enzymes, chemokines, cytokines and growth factors and have therefore been proposed to be essential to invasion, proliferation, angiogenesis and metastases formation. Recent advances in in vivo imaging have yielded new insights into migration of host and cancer cells, however the necessary tools to fully quantify and catalog these interactions are still largely missing. The overall goal of this project is therefore to develop novel in vivo imaging agents with specificity for subtypes of TAM, their monocytic precursors and tissue macrophages. This will be done using powerful library approaches and recently developed nanomaterials capable of detection by multiple imaging modalities and spatial resolutions. In parallel, we will continue the development of imaging agents for other stromal cells ((myo)fibroblasts, NK cells and T cells) to be used in the Weinberg and Jacks projects. In collaboration with the Hynes group as well as other macrophage research groups, we will study the recruitment and fate of monocytes/macrophages in tumors. Finally, targeting TAM as a therapeutic strategy against cancer is an intriguing concept that needs further study. We will therefore measure the effect on tumor growth and metastatic potential following selective anti-TAM therapy. Specifically, we will ask the following questions: 1) What is(are) the direct precursor(s) of TAM, and is there differential participation of TAM subsets in primary and metastatic tumors? 2) What is the involvement of TAM during tumor progression (initiation, invasion, angiogenesis and metastasis)? 3) Does elimination of distinct TAM subsets result in measurable anti-cancer effects? The developed agents and strategies will be designed to be clinically translatable and should support our previous clinical data in glioma that imaging of TAM can have important prognostic and therapeutic implications.